A number of different types of local area network (LAN) systems have been developed and implemented over the last two decades. The LAN systems have different topologies and protocols and various LAN standards have been set by various groups. An overview of industry standard LAN media and protocols is provide in Chapter Six of a book entitled: COMPUTER NETWORKS by U. Black, published by Prentice Hall, Inc. in 1987. This invention will be described in connection with a particular implementation in a RS-485 LAN Bus topology using a layered protocol in accordance with the OSI architectural standard. The electrical characteristics of an RS-485 interface are set forth in EIA STANDARD EIA 485 published by the Electronic Industries Association in April 1983 and available from the Engineering Department of that Association located in Washington, DC. A discussion of the OSI architecture and layered protocols is found in the above referenced book by U. Black in Chapter Three.
Prior art systems which utilize character sense, multiple access protocols generally use collision detection methods to handle the possibility of data transmission collisions on the LAN Bus. A discussion of various aspects of such collision detection schemes is given in Chapter Six of the above referenced book by U. Black.